- Author: Ben Faber
Drought Induced Problems in Our Orchards
Abiotic disorders are plant problems that are non-infective. They are not caused by an organism, but through their damage, they may bring on damage caused by organisms. Think of a tree hit by lightning or a tractor. The damage breaches the protective bark which allows fungi to start working on the damaged area, eventually leading to a decayed trunk. It was the mechanical damage, though that set the process in motion.
Too much or too little water can also predispose a plant to disease. Think of Phytophthora root rot or even asphyxiation that can come from waterlogging or too frequent irrigations.
Salinity Effects from Lack of Water
Lack of water and especially sufficient rainfall can lead to salinity and specific salts like boron, sodium and chloride accumulating in the root zone. This happens from a lack of leaching that removes native soil salts from the root zone or the salts from the previous salt-laden irrigation from the root zone. These salts cause their own kind of damage, but they can also predispose a tree to disorders, disease and invertebrate (insect and mite) damage.
Lack of water and salt accumulation act in a similar fashion. Soil salt acts in competition with roots for water. The more soil salt, the harder a tree needs to pull on water to get what it needs. The first symptom of lack of water or salt accumulation may be an initial dropping of the leaves. If this condition is more persistent, though we start to see what is called “tip burn” or “salt damage”. Southern California is tremendously dependent on rainfall to clean up irrigation salts, and when rain is lacking, irrigation must be relied on to do the leaching
As the lack of leaching advances (lack of rainfall and sufficient irrigation leaching) the canopy thins from leaf drop, exposing fruit to sunburn and fruit shriveling.
Leaf drop and fruit shriveling in avocado.
In the case of sensitive citrus varieties like mandarins, water stress can lead to a pithy core with darker colored seeds, almost as if the fruit had matured too long on the tree.
Total salinity plays an important factor in plant disorder, but also the specific salts. These salts accumulate in the older leaves, and cause characteristic symptoms that are characteristic in most trees. Boron will appear on older leaves, causing an initial terminal yellowing in the leaf that gradually turns to a tip burn.
Often times it is hard to distinguish between chloride, sodium and total salinity damage. It is somewhat a moot point, since the method to control all of them is the same – increased leaching. There is no amendment or fertilizer that can be applied that will correct this problem. The damage symptoms do not go away until the leaf drops and a new one replaces it. By that time hopefully rain and/or a more efficient irrigation program has been put in place.
The Impact of Drought on Nutrient Deficiencies
Salinity and drought stress can also lead to mineral deficiencies. This is either due to the lack of water movement carrying nutrients or to direct completion for nutrients. A common deficiency for drought stressed plants is nitrogen deficiency from lack of water entraining that nutrient into the plant.
This usually starts out in the older tissue and gradually spreads to the younger tissue in more advanced cases.
The salts in the root zone can also lead to competition for uptake of other nutrients like calcium and potassium. Apples and tomatoes are famous for blossom end rot when calcium uptake is low, but we have also seen it in citrus. Low calcium in avocado, and many other fruits, leads to lower shelf life. Sodium and boron accumulation in the root zone can lead to induced calcium deficiencies and increased sodium can also further lead to potassium deficiencies. Leaching can help remove these competitive elements.
Drought Effect on Tree Disease
Drought and salt stress can also lead to disease, but in many cases once the problem has been dealt with the disease symptoms slowly disappear. They are secondary pathogens and unless it is a young tree (under three years of age) or one blighted with a more aggressive disease, the disease condition is not fatal. Often times, in the best of years, on hilly ground these diseases might be seen where water pressure is lowest or there are broken or clogged emitters. The symptoms are many – leaf blights, cankers, dieback, gummosis – but they are all caused by decomposing fungi that are found in the decaying material found in orchards, especially in the naturally occurring avocado mulch or artificially mulched orchards. Many of these fungi are related Botryosphaerias, but we once lumped then all under the fungus Dothiorella. These decay fungi will go to all manner of plant species, from citrus to roses to Brazilian pepper.
Another secondary pathogen that clears up as soon as the stress is relieved is bacterial canker in avocado. These ugly cankers form white crusted circles that ooze sap, but when the tree is healthy again, the cankers dry up with a little bark flap where the canker had been.
Drought Effect on Pests
Water/salt stress also makes trees more susceptible to insect and mite attack. Mites are often predated by predacious mites, and when there are dusty situations, they can't do their jobs efficiently and mites can get out of hand. Mite damage on leaves is often noted in well irrigated orchards along dusty picking rows
Many borers are attracted to water stressed trees and it is possible that the Polyphagous and Kuroshio Shot Hole Borers are more attracted to those trees.
And then we have conditions like Valencia rind stain that also appears in other citrus varieties. We know it will show up in water stressed trees, but we aren't sure what the mechanism that causes this rind breakdown just at color break. Could it be from thrips attracted to the stressed tree or a nutrient imbalance, it's not clear?
Water and salt stress can have all manner of effects on tree growth. It should lead to smaller trees, smaller crops and smaller fruit. The only way to manage this condition is through irrigation management. Using all the tools available, such as CIMIS, soil probes, soil sensors, your eyes, etc. and good quality available water are the way to improve management of the orchard to avoid these problems.
Scroll down for Images
Tip Burn, notice sun burn bottom right hand fruit
Endoxerosis with dried out core
Boron toxicity
Nitrogen deficiency
Blossom end rot
Potassium deficiency
Bot gumming in lemon
Black Streak in Avocado
Bacterial Canker
Citrus red mite
Polyphagous Shot Hole Borer damage on avocado
Valencia Rind Stain
- Author: Ben Faber
Tada
There are some new pest management guidelines out from UC ANR. This is a free publication and you access it as a web page or downloadable PDF document.
These official UC-approved guidelines for pest monitoring techniques, pesticide use, and nonpesticide alternatives for agricultural crops are essential tools for anyone making pest management decisions in the field. This 124-page guideline covers citrus fruit.
A hard copy version of these guidelines can be purchased as Publication 3441P.
The PDF version of this publication is best viewed using the free Adobe® Acrobat® Reader. You can download a free copy of the Acrobat Reader from Adobe Systems Incorporated.
Some users have experienced problems using Preview with these documents; we recommend using the Adobe® Acrobat® Reader.
- Author: Ben Faber
RECOGNIZING NATURAL ENEMIES Proper identification of pests, and distinguishing pests from natural enemies, is essential for effective biological control. Carefully observe the mites and insects on your plants to help discern their activity. For example, some people may mistake syrphid fly larvae for caterpillars. However, syrphid fly larvae are found feeding on aphids and not chewing on the plant itself. If you find mites on your plants, observe them with a good hand lens. Predaceous mites appear more active than plant-feeding species. In comparison with pest mites, predaceous mites are often larger and do not occur in large groups. Consult publications listed in the References to learn more about the specific pests and their natural enemies in your gardens and landscapes. Take unfamiliar organisms you find to your local University of California (UC) Cooperative Extension office, UC Master Gardener Program, or agricultural commissioner office in your county for aid in identification. CONSERVATION: PROTECT NATURAL ENEMIES Preserve existing natural enemies by choosing cultural, mechanical, or selective chemical controls that do not harm beneficial species. Remember, only about 1% of all insects and mites are harmful. Most pests are attacked by multiple species of natural enemies (Table 1), and their conservation is the primary way to successfully use biological control. Judicious (e.g., selective, timing) pesticide use, ant control, and habitat manipulation are key conservation strategies. Ant Control and Honeydew Producers The Argentine ant and certain other ant species are considered pests primarily because they feed on honeydew produced by insects that suck phloem sap, such as aphids, mealybugs, soft scales, psyllids, and whiteflies. Ants protect honeydew producers from predators and parasites that might otherwise control them. Ants sometimes move these honeydew-producing insects from plant to plant (called “farming”). Where natural enemies are present, if ants are controlled, populations of many pests will gradually (over several generations of pests) be reduced as natural enemies become more abundant. Control methods include cultivating soil around ant nests, encircling trunks with ant barriers of sticky material, and applying insecticide baits near plants. See Pest Notes: Ants for more information. Mark Hoddle at UC Riverside is working on a gel formulation to attract ants selectively for their control: http://biocontrol.ucr.edu/hoddle/. Habitat Manipulation Plant a variety of species that flower at different times to provide natural enemies with nectar, pollen, and shelter throughout the growing season. The adult stage of many insects with predaceous larvae (such as green lacewings and syrphid flies) and many adult parasites feed only on pollen and nectar. Even if pests are abundant for the predaceous and parasitic stages, many beneficials will do poorly unless flowering and nectar-producing plants are available to supplement their diet. To retain predators and parasites, grow diverse plant species well adapted to the local conditions and that tolerate low populations of plant-feeding insects and mites so that some food is always available. Other cultural controls that can help natural enemies include reducing dust and properly fertilizing and irrigating. Dust can interfere with natural enemies and may cause outbreaks of pests such as spider mites. Reduce dust by planting ground covers and windbreaks and hosing off small plants that become excessively covered with dust. Avoid excess fertilization and irrigation, which can cause phloem-feeding pests, such as aphids, to reproduce more rapidly than natural enemies can provide control. REFERENCES Dreistadt, S.H., M.L. Flint, and J.K. Clark. 2004. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3359. Flint, M.L. and S.H. Dreistadt. 1998. Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 3386. Rust, M.K. and D.-H. Choe. 2012. Pest Notes: Ants. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7411.
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: |
NATURAL ENEMIES |
|||||
PESTS |
Lacewings |
Lady beetles |
Parasitic flies |
Parasitic wasps |
Predatory mites |
Other Groups and Examples |
aphids |
X |
X |
|
X |
|
entomopathogenic fungi, soldier beetles, syrphid fly larvae |
carpenterworm, clearwing moth larvae |
|
|
|
X |
|
entomopathogenic nematodes |
caterpillars (e.g., California oakworm) |
X |
|
X |
X |
|
Bacillus thuringiensis, birds, entomopathogenic fungi and viruses, predaceous bugs and wasps,Trichogramma spp. (egg parasitic wasps), spiders |
cottony cushion scale |
|
X |
X |
|
|
Cryptochaetum iceryae (parasitic fly), vedalia beetle |
elm leaf beetle |
|
|
X |
X |
|
Erynniopsis antennata (parasitic fly),Oomyzus (=Tetrastichus) spp. (parasitic wasps) |
eucalyptus longhorned borers |
|
|
|
X |
|
Avetianella longoi (egg parasitic wasp) |
eucalyptus redgum lerp psyllid |
|
|
|
X |
|
Psyllaephagus bliteus (parasitic wasp) |
giant whitefly |
X |
X |
|
X |
|
Encarsia hispida, Encarsia noyesi, Entedononecremnus krauteri, andIdioporus affinis (parasitic wasp), syrphid fly larvae |
glassy-winged sharpshooter |
X |
|
|
X |
|
assassin bugs, Gonatocerus spp. (egg parasitic wasps), spiders |
lace bugs |
X |
X |
|
X |
|
assassin bugs and pirate bugs, spiders |
mealybugs |
X |
X |
|
X |
|
mealybug destroyer lady beetle |
mosquitoes |
|
|
|
|
|
Bacillus thuringiensis spp. israelensis, mosquito-eating fish |
psyllids |
X |
X |
|
X |
|
pirate bugs |
scales |
X |
X |
|
X |
X |
Aphytis, Coccophagus, Encarsia, andMetaphycus spp. parasitic wasps |
slugs, snails |
|
|
X |
|
|
Rumina decollata (predatory snail), predaceous ground beetles, birds, snakes, toads, and other vertebrates |
spider mites |
X |
X |
|
|
X |
bigeyed bugs and minute pirate bugs,Feltiella spp. (predatory cecidomyiid fly larvae), sixspotted thrips, Stethorus picipes (spider mite destroyer lady beetle), predatory mites |
thrips |
X |
|
|
X |
X |
minute pirate bugs, predatory thrips |
weevils, root or soil-dwelling |
|
|
|
X |
|
Steinernema carpocapsae andHeterorhabditis bacteriophora(entomopathogenic nematodes) |
whiteflies |
X |
X |
|
X |
|
bigeyed bugs and minute pirate bugs,Cales, Encarsia, and Eretmocerus spp. parasitic wasps, spiders |
Predatory mite going after citrus red mite
/table>- Author: Ben Faber
Here are the top 10 blogs from Topics in Subtropics over the last 5 years. The two earliest and latest pertain to how you select products that will truly help you from amongst all those that are being promoted. Some of these have been around a long time, so that's why they are the most read. Do a Ctrl + click on the URL to read the post.
Title Author Date
A predatory mite
/table>- Author: Ben Faber
TYPES OF NATURAL ENEMIES
Parasites, pathogens, and predators are the primary groups used in biological control of insects and mites (Table 1). Most parasites and pathogens, and many predators, are highly specialized and attack a limited number of closely related pest species. Learn how to recognize natural enemies by consulting resources such as the Natural Enemies Handbook and the Natural Enemies Gallery.
Parasites
A parasite is an organism that lives and feeds in or on a host. Insect parasites can develop on the inside or outside of the host's body. Often only the immature stage of the parasite feeds on the host. However, adult females of certain parasites (such as many wasps that attack scales and whiteflies) feed on and kill their hosts, providing an easily overlooked but important source of biological control in addition to the host mortality caused by parasitism.
Although the term “parasite” is used here, true parasites (e.g., fleas and ticks) do not typically kill their hosts. Species useful in biological control, and discussed here, kill their hosts; they are more precisely called “parasitoids.”
Most parasitic insects are either flies (Order Diptera) or wasps (Order Hymenoptera). Parasitic wasps occur in over three dozen Hymenoptera families. For example, Aphidiinae (a subfamily of Braconidae) attack aphids. Trichogrammatidae parasitize insect eggs. Aphelinidae, Encyrtidae, Eulophidae, and Ichneumonidae are other groups that parasitize insect pests. It's important to note that these tiny to medium-sized wasps are incapable of stinging people. The most common parasitic flies are the typically hairy Tachinidae. Adult tachinids often resemble house flies. Their larvae are maggots that feed inside the host.
Pathogens
Natural enemy pathogens are microorganisms including certain bacteria, fungi, nematodes, protozoa, and viruses that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. In addition to a naturally occurring disease outbreak (epizootic), some beneficial pathogens are commercially available as biological or microbial pesticides. These include Bacillus thuringiensis or Bt, entomopathogenic nematodes, and granulosis viruses. Additionally, some microorganism by-products, such as avermectins and spinosyns are used in certain insecticides; but applying these products is not considered to be biological control.
Predators
Predators kill and feed on several to many individual prey during their lifetimes. Many species of amphibians, birds, mammals, and reptiles prey extensively on insects. Predatory beetles, flies, lacewings, true bugs (Order Hemiptera), and wasps feed on various pest insects or mites. Most spiders feed entirely on insects. Predatory mites that feed primarily on pest spider mites include Amblyseius spp., Neoseiulus spp., and the western predatory mite, Galendromus occidentalis.
AUGMENTATION
When resident natural enemies are insufficient, their populations can sometimes be increased (augmented) through the purchase and release of commercially available beneficial species. However, there has been relatively little research on releasing natural enemies in gardens and landscapes. Releases are unlikely to provide satisfactory pest control in most situations. Some marketed natural enemies are not effective. Many natural enemies are generalist predators and are cannibalistic and feed indiscriminately on pest and beneficial species, thereby reducing their effectiveness.
Only a few natural enemies can be effectively augmented in gardens and landscapes. For example, entomopathogenic nematodes can be applied to control certain tree-boring and lawn-feeding insects. Convergent lady beetles (Hippodamia convergens) purchased in bulk through mail order, stored in a refrigerator, and released in very large numbers at intervals can temporarily control aphids; however, lady beetles purchased through retail outlets are unlikely to be sufficient in numbers and quality to provide control.
Successful augmentation generally requires advanced planning, biological expertise, careful monitoring, optimal release timing, patience, and situations where certain levels of pests and damage can be tolerated. Situations where pests or damage are already abundant are not good opportunities for augmentation.
A classic example of poor timing for augmentative release of predatory mites for control of broad mite in coastal lemon or persea mite in avocado is right now. Pest populations for the most part have soared and releasing predatory mites is little help. Predatory mites need to be releases into a small growing population, so in both of these cases it would have been better to start small, frequent releases early and throughout the spring to knock their populations back.
Adult predatory mite, Euseius tularensis, and citrus red mite.
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